1. Field of the Invention
This invention relates to pump systems for fuel injection systems.
2. Description of the Related Art
Fuel injection systems for diesel engines typically utilize pumps that are cam driven, usually in synchronization with the drive shaft. Consequently, the highest fuel pressure generated at the pump typically occurs at maximum engine speed and load. Lower pressures occur at lower engine speeds and loads. Lower fuel pressures during an injection cycle can result in inefficiencies during injection, resulting in increased emissions and lower power output. It has long been desirable to increase injection pressure at lower engine loads.
Various solutions have been presented, including design changes with respect to nozzle flow, cam phasing, plunger diameter, and plunger velocity among others. For example, increasing plunger diameter can noticeably increase injection pressure at lower engine speeds. A common problem remains, however, and that is that increasing pressure at lower engine speeds also necessarily increases pressure at higher engine speeds. Currently operating pressures at higher speeds are at or near the maximum structural limits of the materials from which the pumps and valve bodies are made, on the order of 29,000 psi (2000 bar). Operating at higher pressures, as would be the case at higher engine speeds and loads, risks failure of the structural components.
There remains a need to control the maximum internal pressure within the injector when the engine is under full load or running at higher speeds.